Remember that Walker kicked Fenton's ass.Also Walker wasn't in Ultimate Enemy. His power spike is still open for interpretation.Walker also seems to be stronger in the Ghost Zone.And Phantoms's out of shape.

All the things you said fall pretty well in under interpretation. If this was the show I feel the outcome would be obvious but in GT it is any one's guess. I could guess his motives for taking on an army single handed. I guess it would come down to: Does bleed want to introduce a new character and a potential new main character or does he prefer to draw dark Danny.

Original Danny could be in the ghost zone because I recall Sam saying he should use his powers to change things for the better and like Pandora (in that one episode) he could be trying to bring order and peace. Also he would be stronger than Dark Danny and Walker, since he has more powers and by now would be an adult.

Plus I could see all the ghosts calling to him for help when Walker became a tyrant.

On the flip side I could see Dark Danny saying something like this-

"You have ruled for too long Walker, you have always been about bringing order, but I have found chaos to be more entertaining and for a chaotic place like the Ghost Zone... I think I would be the better ruler. Say hi to Sam/my past self/my family for me in whatever world comes next."GHOST ZAP